1. Field of the Invention
The present invention relates to an aging device serving as an electronic timer being free from a battery.
2. Description of the Related Art
In recent years, an electronic timer being free from a battery, i.e., a change-over-time device (to be referred to as an aging device) the output of which changes with an elapse of time is beginning to be used in fields of contents distribution, credit cards, rental digital products, rental digital software, and the like.
The aging device has a stack gate structure constituted by a floating gate electrode and a control gate electrode and functions as an electronic timer which measures a predetermined period by a retention characteristic (aging) of electric charges in the floating gate electrode (for example, see JP-A 2004-94922 (KOKAI), JP-A 2004-172404 (KOKAI), and JP-A 2005-310824).
According to the aging device, for example, a tunnel insulating film is changed in thickness to make it possible to change the aging.
However, electric charge leakage from the floating gate electrode changes depending on a manufacturing fluctuation. For this reason, in order to cause the aging device to function as an accurate electronic timer, a complex circuit to eliminate an error generated by the manufacturing fluctuation is required.
As fields in which the aging devices are used spread, the agings of the aging devices must be set to cope with business models, respectively. Since this means that a plurality of production lines of aging devices must be installed in correspondence with the agings, the production cost increases.